Referring to FIG. 1, a schematic diagram of a conventional apparatus for chemical mechanical polishing is shown. The conventional chemical mechanical polishing apparatus includes a rotatable platform 1, a polishing pad 2 covering the rotatable platform 1, a rotatable polishing head 3, and a slurry nozzle 4.
Taking the silicon wafer as an example, a conventional chemical mechanical polishing method can include the following steps: inverting the silicon wafer 5 to make the to-be polished surface of the silicon wafer 5 contacting to the polishing pad 2; pressing the polishing head against the silicon wafer 5; controlling the rotatable platform 1 and the polishing head 3 to rotate; controlling the slurry nozzle 4 to inject slurry 40 to the polishing pad 4; and applying a downward pressure on the polishing head 3 toward the silicon wafer 5. With the rotation of the rotatable platform 1, the slurry 40 flows into the gap between the polishing pad 2 and the to-be polished surface of the silicon wafer 5, and polishes the to-be polished surface of the silicon wafer 5 during the rotational movement of the silicon wafer 5.
During the polishing process, the surface of the polishing pad 2 is gradually being worn and becoming uneven. Therefore, in the polishing process, for a silicon wafer under a certain pressure and at a certain rotational speed, the polishing rate can change over time. Thus, a thickness uniformity of the polished wafer can be decreased. Since the existing chemical mechanical polishing process may lack an effective method for real-time monitoring the thickness of the silicon wafer, the information of the real-time thickness changing of the silicon wafer cannot be obtained. Thus, the problem that a worn polishing pad may significantly decrease the thickness uniformity of the polished silicon wafer may not be discovered in time. If a worn polishing pad is continually used for polishing wafers, it may cause a large number of scrapped wafers, and thereby can reduce the production yield.
The disclosed apparatus and methods are directed to solve one or more problems set forth above and other problems.